This invention relates generally to rotary machines and more particularly, to methods and apparatus for controlling wind turbine blade pitch angles and generator air gap dimensions.
Generally, a wind turbine generator includes a rotor having multiple blades. The rotor is typically mounted to a shaft within a housing, or nacelle, that is positioned on top of a base such as a truss or tubular tower. Utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) can have large rotors, e.g., 30 meters (m) (98 feet (ft)) or more in diameter. Blades, attached to rotatable hubs on these rotors, transform mechanical wind energy into a mechanical rotational torque that drives one or more generators. The generators are generally, but not always, rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the turbine rotor for the generator to efficiently convert the rotational mechanical energy to electrical energy, which is fed into a utility grid. Gearless direct-drive wind turbine generators also exist.
In the generator, rotor components and stator components are separated by an air gap that is typically measured in distance units. During operation, a magnetic field, generated by a plurality of permanent magnets, wound magnets mounted on the rotor, and/or currents induced in the rotor iron passes, through a portion of the air gap defined between the rotor, and the stator. The effective and efficient transmission of the magnetic field through the air gap is at least partly dependent on a predetermined magnitude of an air gap radial dimension, i.e., the radial distance between a rotor surface and a stator surface. However, asymmetric and/or transient loads on the rotor may be introduced via the blades. Such loads may tend to deflect the rotor such that the air gap dimension is reduced and/or altered to be non-uniform.